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PubMed1990

Tangential intracortical pathways and the development of iso-orientation bands in cat striate cortex.

Evidence is accumulating that tangential connections are a prominent feature of cortical organization. In the mammalian visual cortex, these connections appear to be related to columnar systems and theoretical considerations have suggested that they contribute to the development of regularly spaced orientation columns. We tested this assumption and examined whether early cortical lesions affected the formation and layout of the pattern of iso-orientation bands. In the striate cortex of 2-week-old kittens, tangential fiber paths were disrupted unilaterally along the representation of the horizontal meridian either by cuts, or by suction or by implanting pieces of Teflon. At this age, tangential fibers are still growing, orientation selectivity is only poorly developed and 2-deoxyglucose mapping does not yet reveal orientation columns. When the kittens were 7-10 weeks old, the organization of orientation bands was studied with the 2-deoxyglucose technique in flat-mounts of both visual cortices. In addition, kittens from the same litters as the experimental animals, having received the same lesions at the same postnatal day were subjected to neuroanatomical experiments to assess the effect of the lesion on the tangential fibers. These investigations revealed that a small fraction of tangential fibers had grown across the lesion when no mechanical barrier was implanted while disruption of tangential connections was complete in cases who had received Teflon implants. Apart from minor irregularities that were confined to the vicinity of the lesion, the 2-deoxyglucose experiments showed no differences in the pattern of orientation bands between the lesioned and intact hemispheres. In both, the bands extended throughout all cortical layers and their main trajectories were orthogonal to the representation of the vertical meridian. We conclude that at least from two weeks of age onwards, intracortical tangential connections are not necessary for the development of the regular pattern of iso-orientation bands in the striate cortex of cats.

Amidines↗

PubMed1993

Localization of objects in the peripheral visual field.

We investigated visual localization by asking humans to point at visual objects without vision of their hand. The objects were luminous discs, presented stereoscopically at different distances, eccentricities and meridians with respect to the subjects' straight-ahead. Final pointing position was recorded by an electromagnetic search-coil technique. We found that the eccentricity of pointing responses towards peripheral targets was larger when subjects fixated straight-ahead rather than looked at the targets. This outcome confirmed our previous finding that target eccentricity in the peripheral visual field is overestimated. We further found that overestimation increased less than proportionally with target eccentricity, which suggests that the local magnification factor gradually declines in the visual periphery. A quantitative analysis indicated that the magnification factor is about 1.5 at the fovea, and approaches 1.0 at 10 degrees visual angle. Thus, our data support the hypothesis of a peri-foveal magnification effect which gradually subsides with increasing eccentricity. The observed magnification was similar for the horizontal and the vertical meridian. We found that the egocentric distance of pointing responses depends not only on the distance of the object pointed at, but also on the distance of a second object in the visual field. This outcome was in quantitative agreement with the predictions of Foley's model of interactive distance evaluation. Response depth, i.e. the difference in the response distances towards the two objects, was larger if both objects appeared near the center of the visual field rather than if one object appeared in the visual periphery.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Neuronal interactions in cat visual cortex mediated by the corpus callosum.

The article summarizes three sets of physiological and anatomical studies carried out to investigate the structural basis of the functional interactions between visual cortical areas 17 and 18 in the two cerebral hemispheres of cats. (1) The visual field representations in the transcallosal sending and receiving zones are defined. (2) The consequences of severing callosal fibers on the visual field representation at the area 17/18 border are described. (3) Lastly, experiments using cooling to reversibly inactive transcallosal inputs are reported. The observations on the transcallosal sending and receiving zones show that callosal connections of area 17 are concerned with a vertical hour-glass shaped region of the visual field centered on the midline, and this region is doubly represented, once in each hemisphere. The zone represents azimuths within +/- 4 degrees of the midline at the 0 degree horizontal meridian, and azimuths out to +/- 15 to +/- 25 degrees at positions distant from the horizontal meridian. The observations suggest that, in addition to interactions between neurons concerned with positions immediately adjacent to the midline, there are positions, especially high and low in the visual field, where interactions can occur between neurons which have receptive fields displaced some distance from the midline. The extent of this double representation is reduced by approximately 2/3 when the corpus callosum is cut. The retention of some bilateral representation in these animals suggests that there are alternate routes for across-the-midline transmission of visual signals. Or, more likely, there are ganglion cells in temporal retina with crossed projections that make significant contributions to the remaining double representation of the visual field. Lastly, the results obtained using cooling inactivation of transcallosal fibers show that many excitatory and inhibitory circuits are under the direct control of transcallosal fibers in the normally functioning brain. These connections appear to be no different from intrinsic connections of area 17, and they undoubtedly contribute to the binding of the two half-field representations, one in each hemisphere, and perceptual unity across the midline.

Animals↗

PubMed1995

A hand-held keratometer.

Using model eyes the sensitivity to orientation of an Alcon hand-held autokeratometer was assessed after calibration with steel balls. It was concluded that the keratometer should be used in a vertical position (6:00/12:00) in order for axis references to be accurate. Corneal curvature of optometry students was measured using the autokeratometer and a Bausch and Lomb keratometer. The results showed that the autokeratometer was similar to the Bausch and Lomb keratometer in measuring the vertical and horizontal principal meridians, and the axis of the vertical principal meridian. This hand-held keratometer is useful for screening purposes and measuring corneas of infants.

Adult↗

PubMed1980

Local electrical stimulation: effective needling points for suppressing jaw opening reflex in rat.

Effects of electroacupuncture on the jaw opening reflex after tooth pulp stimulation were investigated in lightly anesthetized rats. Electroacupuncture stimulation (45 Hz, 5 msec) was delivered to 8 meridian points and 6 nonmeridian ones for 15 min so as to compare the degree of suppression elicited from each point. Significant suppressive effects on the reflex were observed in the cases of Yin-Hsiang, Ho-Ku and Shou-Sanli stimulation and these effects were antagonized by naloxone. However, stimulation of Hsia-Kuan, Chu-Chih, Neiting and Taichi, although these points were reported to suppress oro-facial or dental pain in man, scarcely produced suppressive effects. On the other hand, stimulation of some nonmeridian points produced moderate analgesic effects as gauged by the jaw opening reflex. The present study revealed that specificity of the meridian points is not absolute, but relative and that Yin-Hsiang, Ho-Ku and Shou-Sanli points were fairly effective in suppressing pulp-evoked jaw opening reflex in rat, which is presumably a noxious reflex. When the jaw opening reflex was evoked by non-pulpal stimulation, electroacupuncture was less effective on the reflex.

Acupuncture Therapy↗

PubMed1984

Retinal ganglion cells that project to the dorsal lateral geniculate nucleus in the macaque monkey.

Horseradish peroxidase was deposited in the optic nerve to retrogradely label and reveal the dendritic form of all classes of ganglion cell, or it was injected into the dorsal lateral geniculate nucleus to reveal only those classes projecting to the thalamus. The results were compared with those of the accompanying paper in which the ganglion cells projecting to the midbrain are selectively revealed. Two major classes of ganglion cells are described, the P alpha and P beta cells. For both classes dendritic field size increases with eccentricity from the fovea and there is no overlap in the two classes at any given eccentricity. Cell body size shows a similar mean difference but with a slight overlap. Both cell bodies and dendritic fields are larger along the temporal horizontal meridian than the nasal horizontal meridian, for P alpha and for P beta cells, but these differences are reduced when naso-temporal differences in ganglion cell density are taken into account, that is, size correlates closely with density. Injections restricted to the parvocellular layers of the lateral geniculate nucleus labelled almost exclusively P beta cells, whereas injections confined to the magnocellular layers labelled almost exclusively P alpha cells. As midbrain injections label no P beta cells and few P alpha cells it can be shown that about 80% of ganglion cells are P beta cells projecting to parvocellular lateral geniculate nucleus, and that about 10% are P alpha cells projecting to magnocellular layers. The coverage factor, that is the number of cells covering each point on the retina, varied from 1.9-2.3 for P beta cells, and from 2-7 for P alpha cells. Comparing the results with those of comparable investigations on cats and rabbits shows a much clearer segregation of the terminal targets of different classes of ganglion cell in monkeys, the greatest difference being the absence in the monkey of a projection to the geniculate from gamma- and epsilon-like cells. Further, axons which branch and innervate both thalamus and midbrain are rare in monkeys but common in other mammals. Comparing the results with those from physiological investigations suggests that the P beta cells correspond to colour-opponent cells, whereas P alpha cells correspond to the achromatic broad-band magnocellular cells.

Animals↗

PubMed1991

Contralateral visual field representation in area 17 of the cerebral cortex of the agouti: a comparison between the cortical magnification factor and retinal ganglion cell distribution.

The cortical representation of the contralateral visual field in area 17 of the agouti's brain was studied by multiunit recording. The borders of area 17 were determined by electrophysiological, cytoarchitectonic and myeloarchitectonic criteria. The results were plotted in flat, bidimensional representations of the cerebral cortex to minimize perspective distortions. The V1 map, a first order topological transformation of the visual field, shows a magnified representation of the horizontal meridian that corresponds to a retinal specialization, the visual streak. The visual field representation has asymmetries that are not directly related to the topography of the retinal ganglion cell density. Whereas the ganglion cell density shows a plateau along the visual streak, the areal cortical magnification factor is higher in the region that corresponds to the intersection of the horizontal and vertical meridians. This suggests functional specializations that are not obvious when one considers the distribution of the whole ganglion cell population but which might be related to the distribution of specific ganglion cell classes.

Animals↗

PubMed1991

The topography of magnocellular projecting ganglion cells (M-ganglion cells) in the primate retina.

The projection from the retina to the dorsal lateral geniculate nucleus in the primate arises from two morphologically distinct types of ganglion cells. The P-ganglion cells project to the parvocellular layers, the M-ganglion cells to the magnocellular layers. We have developed a neurofibrillar stain which stains the M-ganglion cell population with a high degree of selectivity allowing us to map their distribution across the retina. As with other ganglion cell types the M-ganglion cell density peaks close to the fovea and declines towards the periphery. At 1 mm from the fovea the proportion of M-ganglion cells ranges from 6 to 10% and then increases to about 8-10% over much of the retina except along the nasal horizontal meridian. Along the nasal horizontal meridian the percentage increases from 10% at 7 mm eccentricity to 20% or more at higher eccentricities. The increased percentage of M-ganglion cells in the nasal quadrant of the retina correlates with the relatively smaller dendritic trees of M-ganglion cells in this region.

Animals↗

PubMed1996

Models of ganglion cell topography in the retina of macaque monkeys and their application to sensory cortical scaling.

We devised mathematical models of the topography of ganglion cells in the retina of macaque monkeys. The models consisted of a sum-of-three exponentials function fitted to measurements of ganglion cell density made on the nasal horizontal meridian, combined with known anisotropies across the horizontal and vertical meridians by means of elliptic interpolation to provide a full description of their density across the whole of the retinal surface. Integration using standard numerical techniques allowed the number of ganglion cells in arbitrary regions of the retina to be estimated. The topography of actual and effective total ganglion cell populations, and of primate alpha and gamma retinal ganglion cells, was modelled on previously published data. The models were used to test the hypothesis that the retinal projection to the striate cortex in macaque monkeys is peripherally scaled (i.e. merely reflects the eccentricity-dependent variation in density of ganglion cells in the retina) by comparing the cumulative proportion of ganglion cells with the cumulative proportion of cortical area as a function of eccentricity in the visual field. Discrepancies between the two curves indicated that the fovea and immediately surrounding retina are overrepresented in the striate cortex (i.e. there is more cortex per ganglion cell in and near the fovea than in the periphery), and the fact that the discrepancies persisted out to 25-50 degrees of eccentricity showed that the overrepresentation cannot be explained by the lateral displacement of foveal ganglion cells.

Animals↗

PubMed2006

Comparison of single-segment and double-segment Intacs for keratoconus and post-LASIK ectasia.

PURPOSE: To evaluate the efficacy of single-segment Intacs and compare with double-segment Intacs in subjects with post-LASIK ectasia and keratoconus. DESIGN: Retrospective comparative analysis. METHODS: setting: Boxer Wachler Vision Institute, Beverly Hills, California, USA. study population: Thirty-seven eyes of 28 patients with keratoconus and post-LASIK ectasia classified into two groups: single-segment group (17 eyes, 11 patients) and double-segment group (20 eyes, 17 patients). Both groups were matched for age, visual acuity (uncorrected, UCVA; best spectacle-corrected, BSCVA), refractive error (sphere, cylinder, spherical equivalent), and keratometry (K) value (flat, steep, average) by t test for equality of means. intervention: Single- or double-segment Intacs procedure with axis of incision for insertion in the steep axis of manifest refraction. main outcome measure: Improvement of acuity, refractive error, K values, and inferior-superior (I-S) ratio. RESULTS: There was more improvement in UCVA in the single-segment group (nine lines) than the double-segment group (2.5 lines), P < .01; in BSCVA in the single-segment group (2.5 lines) than the double-segment group (<1 line), P < .01; in steep K values in the single-segment group (2.76 diopters +/- 2.68) than the double-segment group (0.93 diopters +/- 2.01), P = .02; and in I-S ratio in the single-segment group (9.51 +/- 7.49) than the double-segment group (4.22 +/- 4.82), P = .01; and greater cylinder decrease after Holladay vector analysis in the single-segment group (5.69 diopters +/- 3.10) than the double-segment group (1.58 diopters +/- 3.09), P < .01. CONCLUSIONS: Single-segment Intacs improved both UCVA and BSCVA by differential flattening of inferior meridian and steepening of superior meridian as reflected by change in I-S ratio.

Adult↗

PubMed2006

Audio-visual dynamic remapping in an endogenous spatial attention task.

Several studies on cross-modal attention showed that remapping processes between sensory modalities occur in the spatial orienting of attention. One hypothesis that accounts for such links is that spatial attention operates upon representations of common locations in the external space. However, convincing evidence only exists for cross-modal links in spatial orienting, leaving the dynamics of these effects unexplored. Four experiments were designed to cope with this issue by having participants being involved in an endogenous orienting task to visual and auditory target stimuli. Targets on invalid trials were embedded into two different kinds of sequences of stimuli: (1) long sequences, wherein three valid trials in one modality preceded the invalid trial in the other modality; (2) short sequences, wherein only one valid trial in one modality preceded the invalid trial in the other modality. Results revealed modality-specific meridian effects in the short sequences, and a significant decrement of the modality-specific meridian effect in the long sequences. The results of these experiments indicate that cross-modal links in visual and auditory spatial attention are based on representations of common locations in the external space across sensory modalities. Moreover, the results strongly support the hypothesis that representations of space are dynamically built and updated according to task demands.

Acoustic Stimulation↗

PubMed2005

Formation of division spindles in higher plant meiosis.

Depolymerisation of the MT cytoskeleton during late prophase makes it impossible to follow the cytoskeleton cycle in centrosomeless plant meiocytes. This paper describes rearrangements of the MT cytoskeleton during plant meiotic spindle formation in normally dividing pollen mother cells in various higher plant species and forms in which the cytoskeleton does not depolymerise at prophase. In such variants of the wild-type, cytoskeleton rearrangements can be observed at late prophase/early prometaphase. Radial MT bundles coalesce in the meridian plane, reorientate tangentially, curve and give rise to a developed ring-shaped perinuclear cytoskeleton system at the meridian. During nuclear envelope breakdown this ring disintegrates and splits into a set of free MT bundles. Three sub-stages of prometaphase are indicated: early prometaphase (disintegration of perinuclear ring and invasion of MTs into the former nuclear area), middle prometaphase or chaotic stage (formation of bipolar spindle fibres), and late prometaphase (formation of bipolar spindle). Analysis of a range of abnormal phenotypes (disintegrated, multiple, polyarchal, chaotic spindles) reveals two previously unknown processes during late prometaphase: axial orientation and consolidation of the spindle fibres.

Cytoskeleton↗

PubMed2004

Radius of curvature and asphericity of the anterior and posterior surface of human cadaver crystalline lenses.

The purpose of this study was to measure the shape of the anterior and posterior surface of human cadaver lenses in situ using a corneal topography system. Measurements were performed on 13 pairs of eyes using the PAR Corneal Topography System (PAR-CTS). The age of the donors ranged from 46 to 93 years, with an average age of 76.4 years. Anterior lens topography was measured after excision of the cornea and iris. Posterior lens topography was measured after sectioning the posterior segment and adherent vitreous. The PAR-CTS files providing raw surface height were exported for analysis. In each surface, 18 meridians separated by 10 degrees were fitted using conic sections to obtain values of the apical radius of curvature (R) and shape factor (p). The average apical radius of curvature and asphericity were R=10.15+/-1.39mm and p=4.27+/-1.39 for the anterior surface and R=-6.25+/-0.79mm and p=-0.64+/-1.85 for the posterior surface. A significant variation of the radius of curvature and shape factor as a function of the meridian angle (lens astigmatism) was found in some lenses. Contrary to previous findings, the anterior lens surface was found to steepen toward the periphery.

Aged↗

PubMed2005

Nutritional manipulation of primate retinas. IV. Effects of n--3 fatty acids, lutein, and zeaxanthin on S-cones and rods in the foveal region.

Lutein and zeaxanthin are xanthophylls selectively accumulated by primate retinas that may protect the macula from age-related macular degeneration. In this project, we manipulated n-3 fatty acids, lutein and/or zeaxanthin levels in the diet and studied their possible outcome on S-cone and rod cell density in the foveal region. Rhesus monkeys (7-16 year, n=17) were fed from birth xanthophyll-free semipurified diets with either adequate or low n-3 fatty acids. Five monkeys were supplemented with lutein and six with zeaxanthin for 6-24 months, while six remained xanthophyll-free until sacrifice. Retinas were embedded in methacrylate and serial 2 microm sections were cut along the vertical meridian. Rod nuclei, and immuno-labelled outer segments of S-cones and rods, were reconstructed and counted in an 8 microm strip. The density profiles were compared with data from control monkeys (n=7) fed a standard laboratory diet. S-cone density profiles were symmetrical along the vertical meridian and the densities decreased rapidly with retinal eccentricity. Rod densities were higher in the superior region than the inferior region in most of the control and experimental animals. Unlike the significant effects observed for retinal pigment epithelial cells of these same monkeys (Leung, I.Y-F., Sandstrom, M.M., Zucker, C.L., Neuringer, M., Snodderly, D.M., 2004. Nutritional manipulation of primate retinas. II. Effects of age, n-3 fatty acids, lutein, and zeaxanthin on retinal pigment epithelium. Invest. Ophthalmol. Vis. Sci. 45, 3244-3256), neither xanthophyll supplementation nor low dietary n-3 fatty acids produced consistent effects on S-cone or rod density profiles of the experimental animals. However, monkeys low in n-3 fatty acids had increased variability of S-cone density in the fovea and low density of foveal rod outer segments. The high variability suggests that the photoreceptors of some animals were resistant to the nutritional manipulations, while others may have been affected. Thus, the photoreceptors appear less sensitive than the retinal pigment epithelium to these nutritional manipulations. However, it is possible that more consistent effects would emerge at a later age or after exposure to stressors such as high light levels.

Animal Nutritional Physiological Phenomena↗

PubMed2004

Treatment of irregular astigmatism with a 213 nm solid-state, diode-pumped neodymium:YAG ablative laser.

PURPOSE: To present the outcome of photorefractive keratectomy (PRK) using a new neodymium:YAG (Nd:YAG) laser in patients with irregular astigmatism. SETTING: Claremont Eye Clinic, Claremont, and the University of Western Australia, Perth, Australia. METHODS: In 3 patients with irregular astigmatism, PRK was performed with a solid-state, 213 nm wavelength, 300 Hz scanning-spot, diode-pumped Nd:YAG ablative laser (CustomVis Pulzar laser system). The 3 patients had had previous PRK with penetrating keratoplasty, astigmatic keratotomy, or limbal relaxing incisions. At 3 and 6 months, best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity (UCVA), manifest refraction, contrast sensitivity, and corneal topography were measured. RESULTS: The first patient had a 1-line improvement in BSCVA and a 4-line improvement in UCVA, a 3.00 diopter (D) decrease in keratometric cylinder, and improvement in contrast sensitivity. The second patient had a 7.00 D decrease in myopia in 1 meridian and a 4.25 D decrease in the refractive cylinder in the other meridian. The third patient had a 2-line improvement in BSCVA, a 5-line improvement in UCVA, a 2.00 D decrease in the refractive cylinder, and improvement in contrast sensitivity. CONCLUSION: The laser's combination of a small spot, a fast pulse rate, and ultrafast tracking/scanning resulted in good results in 3 patients with difficult irregular astigmatism.

Adult↗

PubMed2005

One or 2 Intacs segments for the correction of keratoconus.

PURPOSE: To evaluate the effect of implanting 1 or 2 intracorneal rings (Intacs, KeraVision) as a device to correct, stabilize, and/or improve the best corrected visual acuity in patients with clear cornea keratoconus oriented by the preoperative corneal topography pattern. SETTING: Vissum/Instituto Oftalmológico de Alicante, Miguel Hernandez University, Alicante, Spain. METHODS: In this prospective comparative consecutive study, Intacs segments were implanted in 26 keratoconic eyes with clear central corneas of 19 consecutive patients (9 women and 10 men). Corneas were divided into 2 groups according to the topographic pattern of the cone. Group I included keratoconus not crossing the 180 degrees meridian and Group II included keratoconus crossing the 180 degrees meridian. The Intacs were horizontally placed through a lateral clear corneal incision. According to the corneal topography 1 segment was implanted 0.45 mm inferior in Group I, and 2 segments were implanted, 1 0.25 mm superior and the other 0.45 mm inferior, in Group II. All cases completed a minimum follow-up of 1 year. Differences between preoperative and postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and keratometry were clinically and statistically evaluated. RESULTS: Spherical equivalent error and refractive astigmatism were significantly reduced. The mean keratometric values were reduced following Intacs insertion in both groups. At the end of the first year of the postoperative follow-up, Group I (1 segment) had an improvement in mean UCVA to 20/50 (0.4 +/- 0.22 decimal value), which was statistically significant when compared to the preoperative UCVA of 20/100 (0.2 +/- 0.13 decimal value) (P=.011). Mean BSCVA was 20/32 (0.62 +/- 0.24 decimal value), which was also statistically significant when compared to the preoperative BSCVA, which was 20/50 (0.4 +/- 0.21 decimal value) (P=.002). In Group II (2 segments), UCVA after 1 year was 20/63 (0.34 +/- 0.17 decimal value), which was statistically significant when compared to the preoperative UCVA of 20/400 (0.06 +/- 0.02 decimal value) (P=.001). Mean BSCVA was 20/32 (0.62 +/- 0.27 decimal value), which was significantly better than the preoperative UCVA of 20/50 (0.38 +/- 0.22 decimal value) (P=.001). In 4 eyes, the inferior segment was removed because of partial extrusion during the postoperative follow-up. CONCLUSIONS: Treatment of keratoconus with 1 or 2 Intacs segments oriented by the preoperative corneal topography used in this study proved to be effective in decreasing the corneal steepening and astigmatism and improving BSCVA. Further follow-up is needed to determine the final effect of Intacs on the progression of the corneal disease.

Adult↗

PubMed2007

Topography-guided vertical implantation of Intacs using a femtosecond laser for the treatment of keratoconus.

We report 2 cases of vertical implantation of Intacs (Addition Technology) for the correction of keratoconus with temporal cones. Case 1 was a 16-year-old boy. In the left eye, the refraction was -4.50 x 100, with an uncorrected visual acuity (UCVA) of 0.5 and a best corrected visual acuity (BCVA) of 0.7. The flattest meridian (K1) was 43.7@100 and the steepest meridian (K2), 46.9@10. Case 2 was a 20-year-old woman. In the left eye, the refraction was -6.00 -7.00 x 100, with a UCVA of 0.05 and a BCVA of 0.1; K1 was 51.3@25 and K2, 55.1@115. In each patient, 2 Intacs segments of 0.45 mm and 0.25 mm were inserted in the temporal and nasal regions, respectively. One year postoperatively, the UCVA was 0.7 and 0.3 in Case 1 and Case 2, respectively, and the BCVA was 0.8 and 0.5, respectively. The postoperative refraction was -2.50 x 110 in Case 1 and -5.25 x 95 in Case 2. Based on the localization of the cone, Intacs implantation appeared to improve visual acuity in keratoconic patients.

Adolescent↗

PubMed2004

Spatial mapping of collagen fibril organisation in primate cornea-an X-ray diffraction investigation.

New insights are presented into the collagenous structure of the primate cornea. Wide-angle X-ray diffraction was used to map the fibrillar arrangement and distribution of collagen over three common marmoset corneas. The maps provide a point of reference to help interpret data from pathological corneas or primate models of refractive surgery. The results herein disclose a circum-corneal annulus of highly aligned collagen, 0.5-1.5 mm wide, where the cornea and sclera fuse at the limbus; a feature similar to that observed in human tissue. As in humans, the annulus is not uniform, varying in width, fibril angular spread, and collagen density around its circumference. However, more centrally the marmoset cornea exhibits a preferred lamella orientation in which proportionally more fibrils are oriented along the superior-inferior corneal meridian. This observation is in striking contrast with the situation in human cornea, where there is an orthogonal arrangement of preferentially aligned fibrils. Investigation of a further 16 corneas confirmed that approximately 33% (+/-1%) (n = 76) of fibrils in the central marmoset cornea lie within a 45 degrees sector of the superior-inferior meridian. Implications for the mechanical and optical properties of the cornea are discussed.

Age Factors↗